So-called "55 gallon" drums are used for both storage and transport of numerous liquid or semi-liquid products. Unfortunately, products once placed in such drums undergo little mixing. Some discussion of the construction of "55 gallon" drums can explain this inherent lack of mixing.
A closed head 55 gallon drum consists of a steel cylinder provided with two cylindrical ribs formed by internally cold working the steel cylinder. Circular bottom and top steel lids close both ends of the cylinder with the cylinder sides and circular periphery of the lids being mechanically seamed into a fluid tight joint to close the cylinder. In the case of the closed head drum intended for this application, the top circular lid is provided with a 41/2" diameter central opening or bung. It is through this opening or bung that the barrel is filled with product. After filling the drum is sealed by inserting a cap in the opening and swaging it in.
So-called "open head" 55 gallon drums are known. These drums have a head which is approximately the same diameter as the barrel itself. In this case, one end of the barrel defines a seat for a removable head having the same dimension as the end of the barrel. Typically, when the barrel is filled with product, the head is placed and secured typically with a "bolt ring"--a removable ring which extends around the barrel to protect the removable head at its seat from disruption during storage and transport.
When a barrel is moved, it is either lifted--usually on a pallet with other drums, or rolled. Lifting effects little mixing. Likewise, rolling effects little mixing. When the barrel is rolled, the cylindrical side wall of the drum develops some relative movement to the contained product. However, since the drum is symmetrical about an axis though the center of the cylindrical side walls, and closed by two circular end walls, rolling of the drum occurs with little product movement with respect to the cylindrical side wall of the drum. Thus, rolling of the drum produces little more mixing that lifting of the drum.
Standard 55 gallon drums include an actual capacity of 57 gallons. Usually such drums are loaded with 55 gallons of product to be transported and stored. The remaining space in such 55 gallon drums--that is the remaining 2 gallons of capacity--is left as free space. Normally this space is occupied with a gas and defines a "free surface" at the interface between the gas and the rest of the product contained within the 55 gallon drum. This free surface, however, does little to promote internal mixing.
There is a need for mixing in such 55 gallon drums. This need can best be understood by considering the case of a closed head 55 gallon drum immediate after the drum has been loaded with hot, freshly cooked diced tomatoes.
In the case of hot, freshly cooked diced tomatoes, the barrel is filled with a product which needs to be rapidly cooled. Where the product can be immediately cooled, the cooked and cooled diced tomatoes have a firm consistency and desirable food consistency. In the absence of relatively rapid cooling, the diced tomatoes lose their consistency and be come soft and mush like. The diced tomato product loses its food texture and consequently its value.
Current techniques for rapidly cooling the hot diced tomato product include passing the barrel between a series of stations. At each station, the barrel is rotated, rocked, and simultaneously sprayed with water.
This cooling technique is deficient. As the barrel is rotated, rocked and sprayed, product adjacent the cylindrical side wall of the barrel is rapidly cooled and maintains a firm texture. Unfortunately, product in the central axial portion of the barrel is not cooled as rapidly and continues to cook slowly due to the ambient heat in the barrel until the rocking motion works the product to the walls. The continued cooking produces the undesirable mush texture in the tomato product.